Electro-hydraulic actuator

ABSTRACT

An electro-hydraulic actuator comprising a piston working within a bore, and provided with a piston rod. A system pressure gallery is arranged for the application of system pressure to an annular area between the piston and the piston rod, and another gallery is arranged for applying pressure to the other end of the piston. The latter gallery communicates with the pressure system gallery through a fixed orifice and with a tank outlet through a variable orifice controlled by a flapper, the flapper being balanced with respect to hydraulic pressure and being coupled to the armature of a solenoid and through a feed-back spring to the piston.

United States Patent 1191 Walters Mar. 25, 1975 [22] Filed:

[ ELECTRO-HYDRAULIC ACTUATOR [75] Inventor: Ronald Bernard Walters, Wembley,

England [73] Assignee: Sperry Rand Limited, London,

England Sept. 18, 1973 [2]] App]. No.: 398,412

[30] Foreign Application Priority Data Sept 29, 1972 United Kingdom 45080/72 [52] US. Cl 91/47, 91/387, 91/416 [51] Int. Cl. F15b 13/044 {58] Field of Search 91/47, 49, 385, 387, 416

[56] References Cited UNITED STATES PATENTS 2,574,335 11/1951 Leduc 91/416 x 3,208,352 9/l965 Lucien 9l/387 X 3,664,235 5/1972 Walton .111: 91/387 3,683,748 8/1972 Mahl et al 91/416 Primary Examiner-Irwin C. Cohen Attorney, Agent, or Firm-Barnes, Kisselle, Raisch &

Choate [57] ABSTRACT An electro-hydraulic actuator comprising a piston working within a bore, and provided with a piston rod. A system pressure gallery is arranged for the application of system pressure to an annular area between the piston and the piston rod, andanother gallery is arranged for applying pressure to the other end of the piston. The latter gallery communicates with the pressure system gallery through a fixed orifice and with a tank outlet through a variable orifice controlled by a flapper, the flapper being balanced with respect to hydraulic pressure and being coupled to the armature of a solenoid and through a feed-back spring to the piston.

2 Claims, 1 Drawing Figure 1 ELECTRO-HYDRAULIC ACTUATOR The present invention relates to electro-hydraulic actuators. It is an object of the invention to provide a form of such an actuator which is simple in construction and relatively inexpensive to manufacture.

An electro-hydraulic actuator according to the invention comprises a piston having a piston rod, a system pressure gallery arranged for the application of system pressure to the annular area between the piston and the piston rod, and a gallery for applying pressure to the other end of the. piston, the gallery communicating with the pressure system gallery through a fixed orifice and with a tank outlet through a variable orifice controlled by a flapper, the flapper being balanced with respect to hydraulic pressure and being coupled directly to a solenoid and through a feed-back spring to the piston.

Preferable the flapper is in the form of a disc bearing on the sharpened edge of an outlet tube and the opposite face of the disc is provided with a pressurebalancing tube of the same outside diameter as the sharpened edge of the outlet tube working in a bore in the piston, the pressure in this bore being equalised to be tank outlet pressure, preferably by a passage through the flapper disc. A counter-balancing spring may be provided so as to balance the force of the feedback spring when the actuator is in the fully retracted condition.

The invention will be further described by way of example with reference to the single FIGURE of the accompanying drawing.

The drawing shows an actuator according to the invention in longitudinal section. The actuator comprises a body 1 having a bore 2 for the piston 3. The piston is formed integrally with a piston rod 4, the outer end of which at 5 isprovided with means for coupling it to the apparatus to be actuated.

A system pressure inlet 6 communicates with a gallery 7 by means of which system pressure is applied to the .annular area between the piston and piston rod.

The piston rod is proportioned so that its cross-section is half that of the piston itself, so the system pressure acts effectively over half the piston area.

The pressure inlet 6 also communicates by way of a fixed orifice 8 with a further gallery 9 at the other end of the piston. From this it can escape to tank through a variable orifice formed between the flapper disc 10 and the sharpened edge of an outlet tube 11.

The opposite side of the flapper disc 10 carries a counter-balance tube 12 working in a bore 13 in the piston rod and communicating with tank pressure by means ofa passageway 14 in the flapper disc. The flapper disc is coupled by a rod 15 to the armature of a solenoid l6, and is also acted on by a spring 17, the other end of which is anchored by a clip 18 to the piston.

A balance spring 19 acts on the rod 15 so that under no-load conditions and when the piston is fully retracted inwards the force of the feed-back spring 17 is counter-balanced and the flapper disc 10 rests in equilibrium in a position in which the variable orifice is of substantially the same area as the fixed orifice 8.

A cover 20 encloses the solenoid, and the space within this cover 21 in operation is filled with fluid at tank pressure and communicates with tank by means of a tank port (not visible in the section shown in the FIG: URE).

In operation fluid under pressure is admitted to the system pressure port 6 so that system pressure is applied to the outer end of the piston. The inner end of the piston is subjected to the pressure in the gallery 9 resulting from the inward flow of fluid through the fixed orifice 8 and outward flow through the variable orifice between the flapper l0 and the tube 11, and the balance spring 19 is set up so that this pressure is half the system pressure. The piston is then in equilibrium in its innermost position.

If an electric current is now applied to the solenoid 16, the flapper disc 10 is drawn towards the solenoid, tending to close the variable orifice and raise the pressure in the gallery 9. The piston then moves outwards until the force exerted on the flapper by the feed-back spring 17 substantially counter-balances the pull of the solenoid, allowing the flapper to open and a flow of fluid through the variable orifice to take place. until the piston reaches a new position of equilibrium. The displacement of the piston is therefore substantially pro- I portional to the current flowing through the solenoid.

When the solenoid current is reduced or interrupted the flapper disc moves under the influence of the feedback spring to open the orifice, reducing the pressure in the gallery 9 and causing the piston to move inwards under the pressure in the system pressure gallery 2.

l claim:

1. An electro-hydraulic actuator comprising a body having a bore, a piston working within said bore, and provided with a piston rod, a system pressure gallery arranged for the application of system pressure to the annular area between the piston and the piston rod. and

a gallery forapplying pressure to the other end of the piston, said last-mentioned pressure applying gallery communicating with said pressure system gallery through afixed orifice, an outlet tube secured to said body adjacent said other end of said piston and having a sharpened edge on an end thereof, a flapper in the form of a disc bearing on said tube edge and forming a variable orifice therewith, a solenoid means in said body controlling said flapper, a feedback spring interposed between said other end of said piston and said flapper, a tank outlet open to said outlet tube,

said piston having a closed end bore, the face of said disc opposite to the outlet tube being provided with a pressure balancing tube of the same outside diameter as the sharpened edge of the outlet tube and working in said bore in said piston, said flapper disc having a passage opening on opposite sides thereof to said outlet tube and said pressure balancing tube, respectively, the pressure in said lastmentioned bore being equalized to the tank outlet pressure by means of said passage through said flapper disc. 2. An electro-hydraulic actuator according to claim 2 provided with a counter-balancing spring acting on said flapper disc arranged to balance the force of said feed-back spring when said actuator is in the fully retracted condition. 

1. An electro-hydraulic actuator comprising a body having a bore, a piston working within said bore, and provided with a piston rod, a system pressure gallery arranged for the application of system pressure to the annular area between the piston and the piston rod, and a gallery for applying pressure to the other end of the piston, said last-mentioned pressure applying gallery communicating with said pressure system gallery through a fixed orifice, an outlet tube secured to said body adjacent said other end of said piston and having a sharpened edge on an end thereof, a flapper in the form of a disc bearing on said tube edge and forming a variable orifice therewith, a solenoid means in said body controlling said flapper, a feedback spring interposed between said other end of said piston and said flapper, a tank outlet open to said outlet tube, said piston having a closed end bore, the face of said disc opposite to the outlet tube being provided with a pressure balancing tube of the same outside diameter as the sharpened edge of the outlet tube and working in said bore in said piston, said flapper disc having a passage opening on opposite sides thereof to said outlet tube and said pressure balancing tube, respectively, the pressure in said last-mentioned bore being equalized to the tank outlet pressure by means of said passage through said flapper disc.
 2. An electro-hydraulic actuator according to claim 2 provided with a counter-balancing spring acting on said flapper disc arranged to balance the force of said feed-back spring when said actuator is in the fully retracted condition. 